The physical laws of the universe dictate that oppositely charged particles are attracted to one another. Children are often introduced to this concept early on with magnets, pieces of metal that are either positively charged or negatively charged. Children see these magnets either click together if they are of opposing charges, or repel each other if they share a charge. One way to increase the power of a magnet is by turning it into an electromagnet.
Electromagnets are based on the physical phenomenon of physics called induction. The process of induction causes electrical fields to produce magnetic fields, and magnetic fields to produce electrical fields. This phenomenon was documented in 1831 by the physicist Michael Faraday. His experiments sought to prove that an appropriately designed apparatus could produce electricity from magnetic fields. His discovery that a rotating magnetic field within an electrical field led to the inverse property of induction: that introducing an electric field into a magnetic one would produce additional magnetic fields.
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An electromagnet works by using a source of power to introduce an electrical field into the existing magnetic field, which a magnet naturally produces. By introducing this additional electric field to the existing magnetic field, the electrical field induces an additional magnetic field to the area around the magnet. These two magnetic fields combine to effectively increase the strength of the magnet to attract oppositely charged magnetic forces to it, or repel magnets and charges of the same charge.
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The strength of the electromagnet that results from combining a magnet with the electrical field from a power source is determined by both the strength of the electrical current a power source runs around the magnet and the existing strength of the magnetic field. Whereas the strength of the base magnetic field from the magnet is a static property of the magnet itself, someone tinkering with an electromagnet can increase or decrease the strength of the induced magnetic field by increasing or decreasing the strength of the current from the power source.
The scientific term for the charge a magnet, or any particle for that matter, carries is called the magnet's polarity. A positively charged magnet has a positive polarity, and a negatively charged magnet has a negative polarity. The properties of induction dictate that the polarity of an induced magnetic field will share the polarity of the magnetic field whose interaction with an electrical field generated the induction in the first place. Consequently, creating an electromagnet will magnify the strength of the magnet's base polarity, not change the polarity.